Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

shale, basalt, plagiorhyolite, siltstone, and sandstone age (Tilrnan and others, 1982; Markov and others, 1982). Lower srrucRval
assemblage is an accretionary prism dominated by former oceanic lithosphere, whereas the upper assemblage is interpreted as tbe
base of the Late Jurassic and Early Cretaceous Mainitskiy island uc (Palandzhyan and Dmibenko, 1990). The podiform Cr
deposits in the metallogenic belt (Krassnaya Gora and other deposits) are hosted in the older assemblage whereas the minor
Cyprus massive sulfide deposits are hosted in the younger assemblage. The Mainitskiy tenrane is tectonically linked to the
Alkatvaam accretionary-wedge terrane (Nokleberg and others, 2000).
Mainits Metallogenic Belt of Kuroko
Massive Sulfide Deposits (Belt MA)
Eastern Part of Russian Northeast
The Mainits metallogenic belt of Kuroko massive sulfide deposits (fig. 48; tables 3,4) occurs in the eastern part of the
Russian Northeast. The east-west-trending belt is 170 km long, up to 40 km wide, and is hosted in the Latc Ju~.assk rtod Early
Cretaceous Mainitskiy island-arc terrane (Nokleberg and others, 1994c, 1997~). The significant deposit in the belt is at Ugryumoe
(table 4) (Nokleberg and others 1997% b, 1998).
Ugryumoe Massive Sulfide Deposit
The Ugryumoe deposit consists of miwive suEdw which contain high concentrations of Cu, Zn, Pb, and Au which
occur along a silicified zone up to 3 km long (Oparin and Susheatsov, 1988). The sulfide horizons consists of massive pyrite, and
chalcopyrite, pyrite, and quartz. The suffides occur in a Mesozoic sequence of interbedded basalt, plagiorhyolite, tuff, md
siliceous tuffaceous siltstone. The deposit is interpreted as a possible kuroko massive sulfide deposit and occurs in tbe Hewangian
and Sinemurian Lazov sequences. The sequences contain interbedded basalt, plagiorhyolite, tuffs, and tuff~cem~s sibtone,
Intrusive rocks include granite, plagiogranite, and gabbro. Abundant geological data suggest significant potential f~ additid
massive sulfide deposits in this belt.
Origin of and Tectonic Controls for
Mainits metallogenic belt
The Mainitskiy island-arr: terraae which hosts the Mainib metallogenic belt consists of older and a younger sequences
(Nokleberg and others, 1994c, 1997~). The older sequence consists of: (1) a lower unit of seqmtinite and se~pentinite dlange
which contain fragments of late Paleazoic and early Mesozoic ophiolites, md limestone with spilite and bedded jasptr which
contain Middle and Late Jurassic radiolarim; and (2) an upper unit of graywacke, siltstone, tuff, bedded chert whiuh contain rare
Berriasian and Valanglnian Buchia. Local olistoliths are common add are composed of ophiolik, limatone, pkgbgranice,
andesite, and rhyalrte whch are all metamorphosed to pumpellyite fwb. The younger sequence consists of a thsck assemblage of
Late Juraseic and Early Cretaceous island arc volcanic and sedimentary rocks composed of tholeiitic basalt, mdesitic basalt,
rhyolite, tuf!', breccia, cheit, siltstone, and sandstone. The younger sequence is interpreted as primitive ishd arc sequmce and
contains the Lazov sequence which hosts the rnassive sulfide deposits of the Units metallogenic belt. The Lat% Jurassic and
Early Cretaceous part of the Mainitskiy terrane is iakrpmted as forming in in k&md rrrc which was tectonically Wexi to the
Alkatvaam accretionary-wedge terrane (Nokleberg and others, 2000).
Svyatoy-Nos Metallogenic Belt of
Au-Ag Epithermal Vein Deposlts (W SW)
Northern Part of Russian Northeast
The Svyatoy-Nos metallogenic belt of Au-Ag epithd vein deposits (fig. 48; tables 3,4) occurs in the narrhm patt of
the Russian Northeast. The deposits arc closely related to intermediate and felsic dike with K-Ar isotopic aps of 149 Ma which
are part of Late Jurassic Svyaloy Nos volcanic belt (Bakharev and others, 1998). The epitbermal Au-Ag deposits ia the
metallogenic belt, as at Polevaya, are associated with dikes and small bodies of Early Cretaceous subvolcsmic rhyolite, mauoaite,
and quartz syenite-porphyry (Noklebmg and others 1997% b, 1%). The Svyatoy-Nos metallogenic belt is partly ov~~lain by
Cenozoic sedimentary rocks of the Rimorskaya lowland The sole sigrdcant deposit is at Polevsya (table 4).
Polevaya Au-Ag Polymetallic Vein Wosit
The Polevaya Au-Ag plymetallic vein deposit (NeImisov, 1962; Bakharev and others, 1988) consists of two thin,
subparallel zones of intensely silicified and sericitizzd granodiorite and quartz diorite. The zones range brn 1 to 2 m thick and up
to 500 m long. The zones occw along and near the contact of an Early Cretaceous pluton which forms he core of a oomplnr, Late
Jurassic to Late Cretaceous volcanic-plutonic structure. The major minerals are chalcedony-like crypt~rysblline queutzl, calcite,
pyrite, galena, sphalerite, chalcopyrite, and gold The sulfide content is about 2-3%. The deposit contaias up to 10 dt Au, 10 19/t
Ag, 0.020-1% Pb, 0.050-1% Zn, 0.0054.3% Cu, aad 0.5% Sn.
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